Method for baking and exhausting electron discharge devices



Jan. 27, 1959 R. KoRNER ETAL 2,871,086

` METHOD FOR BAKING AND EXHAUSTING ELECTRON DISCHARGE DEVICES Filed Feb. lO, 1956 3 Sheets-Sheet 1 (Tipping Off 5 and Sealing Area) Bake Oven Exhaust Jam 27, 1959 R. KoRNl-:R ET AL 2,871,036

AMETHOD FOR BAKING AND EXHAUSTING ELECTRON DISCHARGE DEVICES Filed Feb. l0, 1956 I5 Sheets-Sheet 2 Exhaust Step-+I 0cicBake i5" LasMin."

10Min.

Bake

Cool in Oven so Min? T 4o Min.)

L 30 Min.) Y' l Hour 2O Minutes) y Insert Electron Gun and Gun Mount,sea| Gun Mount to Tube ,connect to Exhaust System to Exhaust System Bake Oven 43 (Tipping Off and Sealing Area) Jan. 27, 1959 R. 1 KORNER ETAL 2,871,086 Y METHOD EDR BAKING AND ExHAUsTING EEECTEDN DISCHARGE DEVICES Filed-Feb. 10, 195e :s sheets-sheet s Connect to Exhaust System 43 (TippingOff and vifealing Area) WITNESSES INVENTORS ATTORNEY United States Patent O METHOD FOR BAKING AND EXHAUSTING ELECTRON DISCHARGE DEVICES Renzo L. Korner, Montour Falls, and Gilbert N. Rieger and William H. McCurdy, Horseheads, N. Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 10, 1956, Serial No. 564,826

6 Claims. (Cl. 316-4) operation will take at least four hours, exclusive of the time consumed in sealing the electron gun mount into the neck of the cathode ray tube. The considerable time involved in this operation creates the possibility of the phosphor screen or the bulb of the tube becoming contaminated. Also, cooling after the initial heating step permitsv absorption and condensation of gases, water vapor and other contaminants. Contamination of this sort leads to'inferior tubes lacking desirable long-life characteristics.

In general, our invention comprises a method of performing the baking operations without cooling, which results in a time-saving of over 60% and produces tubes having considerably improved long-life characteristics.

Accordingly, it is an object of our invention to provide an improved method of making electron discharge devices having internal phosphor coatings.

,lt is another object to provide an improved ymethod of baking and exhausting such electron discharge devices.

It is a further object to provide an improved method of making such electron discharge devices, which devices, by virtue of our improved method, will have superior long-life characteristics.

I-t is an additional object to Vprovide an improved method of baking and exhausting such electron discharge devices, which method will result in a time reduction of over 60% over previous baking and exhaustion methods.

These and other objects of our invention will be apparent from the following description, taken in accordance with the accompanying drawing throughout which like reference characters indicate like parts, which drawing forms a part of this application and in which:

Figure l is a schematic side sectional view of a typical cathode ray tube;

Fig. 2 is a curve representing the times and temperatures involved in prior art methods of baking and exhausting electron discharge devices; f

Fig. 3 is a curve representing the times and temperatures involved in one embodiment of our method of baking and exhausting electron discharge devices;

Fig. 4 is a curve representing the times and tempera-.

tures involved in another embodiment of our method of baking and exhausting electron discharge devices;

Fig. 5 is a schematic representation of the embodiment of our invention shown in Fig. 3;

' Fig. 6 is a schematic representation of an embodiment of our invention shown in Fig. 4; and

ICC

' bodiment of our invention shown in Fig. 4.

A typical completed cathode ray tube 11', as shown in Fig. 1, includes an envelope or bulb member 45, an electron gun member 47 and a uorescent screen member 49. The bulb member 45 includes a face plate por# tion 51 and a neck portion 53. Also shown is the base member 55.

In Fig. 2 there is shown a curve representing times and temperatures involved for a typical prior art method of baking and exhausting a cathode ray tube. An aluminized iiuorescent screen member 49 is made by setting phosphor material in the tube, depositing a support lilm over the phosphor and evaporating a thin aluminum layer upon the support lm. The tube is then inserted in an' oven, raised to a temperature of 400 C. in 40 minutes, and is baked at the temperature of 400 C. for 30 minutes. The tube is cooled in the oven for one hour and 20 minutes, at which time it has reached a temperature of approximately 250 C., and then it is cooled in air for 30 minutes to bring it to a temperature below C. Next the electron gun member 47 and gun mount are inserted into the neck portion 53 of the bulb member 45, the gun mount is sealed to the bulb member and the exhaust tubulation attached to the gun mount is connected to the exhaust system. The exhaust step consists of exhausting the tube to the desired pressure while heating it in an oven for l5 minutes to bring it to 400 C., baking for 10 minutes at 400 C. and cooling in air for approximately 35 minutes to bring it to a temperature of about C. The total time involved is about 4 hours plus the time needed to seal the gun mount into the neck of the tube.

One embodiment of our method of baking and exhausting a cathode ray tube is shown in Figs. 3 and 5. In our invention, a phosphor screen, a support layer and a thin aluminum lm have been placed in a cathode ray tube bulb member as discussed in a later portion of this specification. The uncompleted cathode ray tube 11 is unloaded from the pre-bake-exhaust portion 13 of a conveyor 14 and is loaded into an enclosure member 15 which may be constructed of cold rolled steel. This enclosure member 15 is supported by a dolly member 17. The enclosure member 15 with the cathode ray tube 11 inside it, is placed in a bake oven 19 where it is heated for 15 miuutesto bring the tube to a temperature of 400 C. and then baked for 30 minutes at a temperature of 400 C.' During the bake step, the neck portion of the tube is left open to the atmosphere. Without cooling, the electron gun member 47 and gun mount are inserted into the neck portion 53 of the bulb member 45. The gun mount is sealed to the bulb member 45. The sealing operation is done in the sealing area 21. The exhaust system is carried in the exhaust cart 23, upon which the enclosure member 15 containing tube 1l is placed. The exhaust tubulation attached to the gun mount is then connected to the exhaust system. The enclosure member 15 is then inserted into the exhaust oven 25 and is exhausted to the desired pressure while being heated at 400 C. for 28 minutes and then cooled for 22 minutes, which brings it to a temperature of approximately 100 CQ The exhaust tubulation is then tipped ofi and sealed in a tip-ott area 27. The exhaust cart is returned to its original position along the cart return path 29. During the cooling portion of the exhaust step, the electron gun member 47 may be heated by radio-frequency heating and the cathode conversion process may take place. Finally, the finished cathode ray tubefll' is unloaded from the enclosure member 15 and placed upon the post-b ake-exhaust portion'33 of the conveyor 14. It is to-be. noted `that in this particular embodiment, the electron gun member 47 is inserted and sealed between thel bake step and the exhaust step, but that there is no cooling between the bake step and the exhaust step.

Another embodiment of our invention is shown in Figs. 4 and 6. In this embodiment, the phosphor material has been inserted in the bulb, the support layer has been placed upon the phosphor layer and the thin aluminum film has been evaporated upon the support layer. Also, the electron gun member `47 and gun mount have been inserted into the neck portion 53 of the bulb member 45, and the gun mount has been sealed. to the bulb member 4S. The uncompleted cathode ray tube 1l is then unloaded from the pre-bake-exhaust conveyor' i4 and placed in the enclosure member l5', which is attached to the exhaust cart 23. During the bake step, the exhaust tubulation of the cathode ray tube 1l is left open to the atmosphere. The enclosure member i5 is then inserted into the bake oven 35 and is heated for l5 minutes to a temperature of 400 C. Then the tube in the enclosure member is baked for 30 minutes at the temperature of 400 C. Without removing the enclosure member 1S from the oven, the exhaust tubulation of the cathode ray tube ll is connected to the exhaust system carried by the exhaust cart 23. The tube in the enclosure is then baked for 28 minutes at 400 C. in the exhaust oven 39 as it is being exhausted. The tube in the enclosure is cooled for an additional 22 minutes on a cooling conveyor 4l while it is still being exhausted to the desired pressure and reaches a temperature of approximately 100 C. During this cooling portion of the exhaust step, the electron gun member 47 may be heated by radiofrequency heat, and the cathode conversion process may be accomplished. Then the exhaust tubulation is tipped off and sealed in the sealing area 43, and the finished cathode ray tube 1l is unloaded from the enclosure member and placed upon the post-bake-exhaust conveyor 33.

Still another embodiment of our invention is shown in Figs. 4 and 7. ln this embodiment, the phosphor material has been inserted in the bulb, the support layer has been placed upon the phosphor layer and the thin aluminum lm has been evaporated upon tho support layer. Also, the electron gun member 47 and gun mount have been inserted into the neck portion 53 of the bulb member 45, and the gun mount has been sealed to the bulb member 45. The uncompleted cathode ray tube ll is then unloaded from the pre-bake-exhaust conveyor i3 and placed on the exhaust cart 23. During the bake step the exhaust tubulation of the cathode ray tube ll is left open to atmosphere. The tube 11 is then inserted into the bake oven 36 and is heated for l5 minutes to a temperature of 400 C. The tube l1 is baked for 30 minutes, at the temperature of 400 C. The exhaust tubulation of the cathode ray tube ll is connected to the exhaust system carried by the exhaust cart 23. The tube is then baked for 28 minutes at 400 C. in the exhaust oven 38 as it is being exhausted. The tube ll is cooled in the oven 38 for an additional 22' minutes While it is still being exhausted to the desired pressure and reaches a temperature of approximately 100. During this cooling portion of the exhaust step, the electron gun member 47 may be heated by radio-frequency heat, and the cathode conversion process may be accomplished. Then the cxhaust tubulation is tipped olf and sealed in the sealing area 43, and the finished cathode ray tube 11 is unloaded from the exhaust cart 23 and placed upon the post-bakeexhaust conveyor 33.

In the manufacture of cathode ray tubes, a phosphor material is settled upon the face plate portion 51 of the tube. Most modern cathode ray tubes for television receivers have a thin aluminum film behind the phosphor screen to increase the light output of the tube and prevent destruction of the phosphor screen due to ion bombardment.

A method of forming this thin aluminum lm involves depositing a support lm of an organic material upon the phosphor material, evaporating a thin film of aluminum upon the support :lilrn and removing the support film by heating. Materials which we have found to be suitable for support films include thermally depolymerizable resins such as polybutyl methacrylate. A material of this type will depolymerize upon heating, forming the monomer. In the specific example given, butyl methacrylate will be formed and as butyl methacrylate vaporizes at a temperature of 300 C.-400 C., it will be remove-d as a gas during the bake step. Thus, we use a film material which does not need to be oxidized to be removed and, therefore, does not need to be flushed with air or oxygen. ln the embodiment of our invention shown in Figs. 4 and 6 in which the electron gun member 47 is sealed in the cathode ray tube bulb member 45 before the bake step, a flush of air or oxygen would cause excess oxidation of the electron gun parts. We have found, however, the amount of air in the tube at the start of the bake step is insufficient to cause oxidation of the gun parts, particularly since the butyl methacrylate monomeric gas formed during the bake step and the expansion of the air itself due to heat acts to force most of the air and water vapor from the tube at a relatively low temperature before the harmful oxidation can occur.

lf the exhaust system is connected to the tube during the bake step, we have found that tubes are not properly degassed because the gas driven off during the bake step tends to overload and contaminate the exhaust system. Also, the butyl methacrylate monomer, in the quantities formed during the bake step, has harmful effects on the exhaust system.

The electron gun member 47 may be sealed to the tube before the bake step as in the embodiment shown in Figs. 4 and 6, because we have found that the monomeric butyl methacrylate driven ott" does not have any harmful effects on the electron gun member 47 itself. However, if the tube is exhausted during the bake step, the cathodes of the electron gun have poor emissivity, probably because the cathode binder material is reduced to elemental carbon rather than carbon dioxide or carbon monoxide. The elemental carbon tends to reduce the emissivity of the cathode.

Of course, our invention is not limited to use in cathode ray tubes but may be applied to any electron discharge device containing a phosphor coating or screen. For example, electric uorescent lamps may be made by the method of our invention. A thermally depolymerizable resin, such as polybutyl methacrylate is used as the phosphor binder material and the lamp is heated with one end of the lamp being exposed to the atmosphere. The bake step degasses the lamp, depolymerizes the resin binder and vaporizes the monomer formed. Without cooling the lamp, the exhaust system is connected to it, and the lamp is exhausted. The lamp is baked for a portion of the exhaust step and cooled for the remainder of the step. Finally, the lamp is tipped olf and sealed. The lamp is baked before it is 'connected to the exhaust system, and there is no cooling between the bake and exhaust steps for the same reasons as previously discussed in relation to cathode ray tubes.

-It is readily seen from Figs. 2-4 that the length of the baking step is considerably reduced by our invention because of the omission of the cooling portion of the baking step. Also, the total exhaust time may be reduced by at least one-sixth because a tube at 400 C. may be exhausted faster than a tube which starts at a lower temperature and is heated to 400 C.

Although the quality of a tube made by our method may not outwardly appear to be appreciably different from one made by prior art, tests show that tubes made by our methods have a considerably longer life. This long life may be attributed to the lack of contamimnants and the more thorough exhaust which occurs because the tube is at a high temperature for a longer time as shown in Figs. 2-4.

that it is not so limited, but is susceptible of various changes and modications without departing from the spirit and scope thereof.

We claim as our invention:

1. A method of making an electron discharge device Ihaving a phosphor coating on at least a portion of the interior of said device, said method including the steps of heating the device for a iirst time interval and simultaneously maintaining said device open to the atmosphere during said tirst time interval to expel large portions of any undesirable vaporizable material from said phosphor coating and said device, connecting an exhaust system to said electron discharge device while maintaining the temperature of the device at approximately the temperature which the device reached during the heating step, exhausting said electron discharge device during a second time interval and heating said electron discharge device for at least a portion of said second time interval thereby expelling substantially all of said vaporizable material.

2. A method of making a cathode ray tube, said method including the steps of placing a phosphor material within said tube said phosphor material having undesirable vaporizable material therein, heating said tube during a flrst time interval and simultaneously maintaining said tube open to the atmosphere during said first time interval to remove a portion of said undesirable vaporizable material from said phosphor material and from said tube, connecting an exhaust system to said tube While maintaining the temperature of said tube at approximately the temperature which the tube attained during the heating step, and exhausting said tube for a second time interval while heating said tube for at least a portion of said second time interval thereby removing substantially' all of said undesirable vaporizable material.

3. A method formaking a cathode ray tube having a neck portion and an electron gun mount member having an exhaust tubulation member, said method including the steps of placing a phosphor material in said tube, coating said phosphor material with a material containing a thermally removable resin, placing an aluminum hlm over said thermally removable resin material, sealing said electron gun mount member into the neck portion of said cathode ray tube, heating said cathode ray tube for a iirst time interval and simultaneously maintaining said exhaust tubulation member open to the atmosphere during said first time interval to thereby remove large portions of said thermally removable resin material and to partially degas said cathode ray tube, connecting an exhaust system to said exhaust tubulation member While keeping said cathode ray tube at approximately the same temperature as it reached during the above heating step, exhausting said cathode ray tube for a second time interval While heating said cathode ray tube for at least a portion of said second time interval thereby removing substantially all of said thermally removable resin material and substantially completely degassing said cathode ray tube, and tipping oi and sealing said exhaust tubulation member.

4. A method of making Va cathode ray tube having a neck portion and an electron gun mount member having an exhaust tubulation member, said method including the steps of placing a phosphor material in said tube, coating said phosphor material with a material containing a thermally removable resin, placing an aluminum film over said thermally removable resin material, sealing an electron gun mount member into the neck portion of said cathode ray tube, heating said cathode ray tube for approximately l5 minutes to bring said tube to a temperature of approximately 400 C., heating said tube at a temperature of approximately 400 C., for approximately 30 minutes and simultaneously maintaining said exhaust tubulation member open to the atmosphere during both the previous heating steps thereby removing large portions of said resin material, connecting an exhaust system to said exhaust tubulation member while keeping said cathode ray tube at approximately 400 C., exhausting said cathode ray tube for approximately 50 minutes, heating said cathode ray tube at a temperature of approximately 400 C., for approximately 28 minutes of said 50 minutes, cooling said cathode ray tube for approximately 22 minutes of said 50 minutes, thereby removing substantially all of said resin material, and substantially completely degassing said cathode ray tube and tipping off and sealing said exhaust tubulation member.

5. A method of making a cathode ray tube having a neck portion and an electron gun 'mount having an exnaust tubulation member, said method including the steps of placing a phosphor material in said tube, coating said phosphor material with a material containing a thermally removable resin material, placing an aluminum lm over said thermally removable material, heating said cathode ray tube to a temperature of approximately 400 C. in approximately l5 minutes, hea-ting said cathode ray tube at a temperature of approximately 400 C. for approx-imately 30 minutes and simultaneously maintaining said neck portion open to the atmosphere during the previous two heating steps thereby removing large portions of said resin material, inserting said electron gun mount in said neck portion', sealing said gun mount to said neck portion, connecting an exhaust system to said exhaust tubulation member, keeping said cathode ray tube at a temperature of approximately 400 C. during said inserting, sealing and connecting steps, exhausting said cathode ray tube for a period of Vapproximately 50 minutes, heating said cathode ray tube at a temperature of approximately 400 C. for approximately 28 minutes of said 50 minutes, cooling said cathode ray tube for approximately 22 minutes of said 50 minutes, thereby removing substantially all of said resin material and substantially completely degassing said cathode ray tube and tipping off and sealing said exhaust tubulation member.

6. A method of making an electric fluorescent lamp having a bulb and an exhaust tubulation, said method including the steps of coating a portion of said bulb with a uorescent material containing a thermally removable resin binder material, heating said bulb during a rst time interval and simultaneously maintaining said exhaust tubulation open to the atmosphere during said iirst time interval so that large portions of said resin binder material are removed and said lamp bulb is partially degassed, connecting an exhaust system to said exhaust tubulation while keeping said bulb at the same temperature as it reached during the above heating step, exhausting said bulb during a second time interval, and heating said bulb for at least a portion of said second time interval thereby removing substantially all of said resin binder material and substantially completely degassing said lamp.

References Cited in the tile of this patent UNITED STATES PATENTS Karasick Oct. 14, 1941 

